The metabolism of 7,10,13,16,19-docosapentaenoic acid to 4,7,10,13,16,19-docosahexaenoic acid in rat liver is independent of a 4-desaturase

Eicosapentaenoic acid and docosahexaenoic acid from fish oils: differential associations with lipid responses

Fish-oil supplementation can reduce circulating triacylglycerol (TG) levels and cardiovascular risk. This study aimed to assess independent associations between changes in platelet eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and fasting and postprandial (PP) lipoprotein concentrations and LDL oxidation status, following fish-oil intervention. Fifty-five mildly hypertriacylglycerolaemic (TG 1·5–4·0 mmol/l) men completed a double-blind placebo controlled cross over study, where individuals consumed 6 g fish oil (3 g EPA+DHA) or 6 g olive oil (placebo)/d for two 6-week intervention periods, with a 12-week wash-out period in between. Fish-oil intervention resulted in a significant increase in the platelet phospholipid EPA (+491 %,P<0·001) and DHA (+44 %,P<0·001) content and a significant decrease in the arachidonic acid (-10 %,P<0·001) and γ-linolenic acid (-24 %,P<0·001) levels. A 30 % increase inex vivoLDL oxidation (P<0·001) was observed. In addition, fish oil resulted in a significant decrease in fasting and PP TG levels (P<0·001), PP non-esterified fatty acid (NEFA) levels, and in the percentage LDL as LDL-3 (P=0·040), and an increase in LDL-cholesterol (P=0·027). In multivariate analysis, changes in platelet phospholipid DHA emerged as being independently associated with the rise in LDL-cholesterol, accounting for 16 % of the variability in this outcome measure (P=0·030). In contrast, increases in platelet EPA were independently associated with the reductions in fasting (P=0·046) and PP TG (P=0·023), and PP NEFA (P=0·015), explaining 15–20 % and 25 % of the variability in response respectively. Increases in platelet EPA+DHA were independently and positively associated with the increase in LDL oxidation (P=0·011). EPA and DHA may have differential effects on plasma lipids in mildly hypertriacylglycerolaemic men.

Failure of conjugated linoleic acid supplementation to enhance biosynthesis of docosahexaenoic acid from alpha-linolenic acid in healthy human volunteers

A rate-limiting step in docosahexaenoic acid (DHA) formation from alpha-linolenic acid (ALA) involves peroxisomal oxidation of 24:6n-3 to DHA. The aim of the study was to determine whether conjugated linoleic acid (CLA) would enhance conversion of ALA to DHA in humans on an ALA-supplemented diet. The subjects (n=8 per group) received daily supplementation of ALA (11g) and either CLA (3.2g) or placebo for 8 weeks. At baseline, 4 and 8 weeks, blood was collected for plasma fatty acid analysis and a number of physiological measures were examined. The ALA-supplemented diet increased plasma levels of ALA and eicosapentaenoic acid (EPA). The addition of CLA to the ALA diet resulted in increased plasma levels of CLA, as well as ALA and EPA. Plasma level of DHA was not increased with either the ALA alone or ALA plus CLA supplementation. The results demonstrated that CLA was not effective in enhancing DHA levels in plasma in healthy volunteers.

Ácidos graxos poliinsaturados ômega-3 e ômega-6: importância e ocorrência em alimentos

Os ácidos graxos poliinsaturados abrangem as famílias de ácidos graxos ômega-3 e ômega-6. Os ácidos graxos de cadeia muito longa, como os ácidos araquidônico e docosaexaenóico, desempenham importantes funções no desenvolvimento e funcionamento do cérebro e da retina. Esse grupo de ácidos graxos não pode ser obtido pela síntese de novo, mas pode ser sintetizado a partir dos ácidos linoléico e alfa-linolênico presentes na dieta. Neste artigo são considerados os principais fatores que podem inibir a atividade das enzimas dessaturases envolvidas na síntese dos ácidos graxos de cadeia muito longa. São apresentadas as recomendações da razão ômega-6/ômega-3 na dieta, propostas em diversos países, sendo verificada a convergência para o intervalo de 4 a 5:1. São relacionados alimentos que podem contribuir para aumentar a ingestão do ácido alfa-linolênico e dos ácidos graxos de cadeia muito longa. A essencialidade dos ácidos graxos de cadeia muito longa é muito dependente do metabolismo do indivíduo, sendo que a razão n-6/n-3 da dieta exerce grande influência nesse sentido.

Innovative Dietary Sources of N-3 Fatty Acids

It is now established that dietary n-3 polyunsaturated fatty acids (PUFAs) are involved in health promotion and disease prevention, particularly those traditionally derived from marine sources (e.g., eicosapentaenoic acid and docosahexaenoic acid). A number of organizations have made specific recommendations for the general population to increase their intakes of these nutrients. In response to and along with these recommendations, n-3 PUFAs are being incorporated into nontraditional food sources because of advances in the technology to safely enrich/fortify our food supply. Fatty acid compositions of traditional oils (e.g., canola and soybean) are being genetically modified to deliver more highly concentrated sources of n-3 PUFA. The advent of algal sources of docosahexaenoic acid provides one of the few terrestrial sources of this fatty acid in a concentrated form. All of this is possible because of newer technologies (microencapsulation) and improved processing techniques that ensure stability and preserve the integrity of these unstable fatty acids.

Docosahexaenoic acid in red blood cells of term infants receiving two levels of long-chain polyunsaturated fatty acids

OBJECTIVES

A randomized, double-blind, prospective trial assessed effects of different formula levels of polyunsaturated fatty acids on blood phospholipid docosahexaenoic (DHA; 22:6omega3) and arachidonic acids (ARA; 20:4omega6) in term infants at 120 days of age.

METHODS

Healthy, formula-fed term infants (n = 78) were randomized to 1) routine milk-based formula with 8 mg DHA, 21 mg ARA, 110 mg alpha-linolenic (ALA; 18:3omega3), and 1,000 mg linoleic acids (LA; 18:2omega6) per 100 kcal (Lower-long-chain polyunsaturated fatty acids [LCPUFA]; n = 39) or 2) routine milk-based formula with 17 mg DHA, 34 mg ARA, 85 mg ALA, and 860 mg LA per 100 kcal (Higher-LCPUFA; n = 39). Fatty acid methyl esters from red blood cell (RBC) and plasma phospholipid fractions were assessed using capillary column gas chromatography.

RESULTS

Compared with infants fed Lower-LCPUFA formula, the Higher-LCPUFA group had significantly greater percentages of fatty acids as DHA in RBC phosphatidylethanolamine (PE), RBC phosphatidylcholine (PC), total RBC, and plasma phospholipids (P < 0.001). Infants fed Lower-LCPUFA formula had higher percentages of precursor omega6 fatty acids in the desaturation/elongation pathway but lower percentages of ARA (RBC PE, RBC PC, and plasma phospholipid, P < 0.001; total RBC, P = 0.017) compared with the Higher-LCPUFA group.

CONCLUSIONS

Greater amounts of dietary ALA do not produce as great an increase in DHA in blood lipids as preformed dietary DHA. Infants fed DHA at levels similar to human milk had significantly greater percentage of DHAat 120 days of age compared with the Lower-LCPUFA group despite higher precursor levels of ALA.

Vitamin A deficiency enhances docosahexaenoic and Osbond acids in liver of rats fed an α-linoleic acid-adequate diet

The synthesis of docosahexaenoic (DHA, 22:6n-3) and Osbond acid (OA, 22:5n-6) is regulated by the heterodimer of peroxisome proliferator-activated receptor and retinoid X receptor (RXR). 9-Cis retinoic acid, a metabolite of vitamin A, is the most potent ligand of RXR. We tested whether vitamin A deficiency impairs DHA and OA synthesis in rats fed a vitamin A- and alpha-linolenic acid (ALA)-sufficient (VASALAS), vitamin A-sufficient and ALA-deficient (VASALAD), vitamin A-deficient and ALA-sufficient (VADALAS), or vitamin A- and ALA-deficient (VADALAD) diet. After 7 wk of feeding, liver and colon choline (CPG) and ethanolamine (EPG) phosphoglyceride FA were analyzed. The VADALAS compared with the VASALAS rats had elevated levels of both DHA (P< 0.05) and OA (P < 0.005) in liver CPG and EPG. In contrast, the VADALAD group had a lower DHA (P < 0.01) and higher OA (P < 0.005) level in CPG and EPG of both tissues than their VASALAD counterparts. ALA deficiency reduced DHA and enhariced OA levels in liver and colon CPG and EPG in both the vitamin A-sufficient (VASALAS vs. VASALAD) and -deficient (VADALAS vs. VADALAD) rats (P < 0.005). The study demonstrates that ALA deficiency reduced DHA and enhanced OA levels in tissue membranes, and dietary vitamin A deficiency has a profound effect on membrane DHA and OA in rat tissues. Both vitamin A and DHA are involved in a myriad of vital physiological functions pertaining to growth and development and health. Hence, there is a need for a further study to unravel the mechanism by which vitamin A influences membrane DHA and OA.

Primary open-angle glaucoma patients have reduced levels of blood docosahexaenoic and eicosapentaenoic acids

The aetiology of primary open-angle glaucoma (POAG), which is the commonest cause of non-remediable blindness and visual impairment, is not well understood. Nevertheless, increased intraocular pressure, and vascular factors such as ocular blood flow deficits are thought to be risk factors. There is evidence of decreased optic nerve blood velocity and increased red blood cell aggregability in POAG. These factors are influenced by fatty acids. We have investigated if glaucoma patients have abnormal blood fatty acid composition. Patients with POAG (n=10) and their healthy siblings (n=8) were enrolled. Compared with their healthy siblings, the glaucoma patients had reduced eicosapentaenoic (EPA, P<0.01), and docosahexaenoic (DHA, P<0.05) fatty acids and total omega3 long-chain polyunsaturated fatty acids (LCPUFA) (P<0.05) in red cell choline phosphoglycerides (CPG); decreased EPA (P<0.05) in ethanolamine phosphoglycerides (EPG); lower EPA (P<0.05) and total omega3 LCPUFA (P<0.05) in serine phosphoglycerides (SPG). Similarly, they had reduced EPA, DHA and total omega3 LCPUFA in plasma CPG (P<0.005) and triglycerides (P<0.05). These findings may be significant, since EPA and DHA could modulate impaired systemic microcirculation and ocular blood flow and optic neuropathy, which are the main physiological changes associated with glaucoma.

Dietary enrichment with omega-3 polyunsaturated fatty acids reverses age-related decreases in the GluR2 and NR2B glutamate receptor subunits in rat forebrain

Ageing is associated with a decrease in the brain content of omega-3 polyunsaturated fatty acids (PUFA), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and with decreased neuroplasticity. The glutamate receptor subunits GluR2 and NR2B play a significant role in forebrain synaptic plasticity. We investigated GluR2 and NR2B in the aged prefrontal cortex, hippocampus and striatum, and tested if treatment with a preparation containing EPA and DHA can reverse age-related changes. The study compared adult and old (3-4 and 24-26 month) rats, and the latter were fed a standard diet or a diet supplemented for 12 weeks with omega-3 PUFA at 270mg/kg/day (ratio EPA to DHA 1.5:1). Ageing was associated with decreases in the GluR2 and NR2B subunits in all structures. These decreases were fully reversed by omega-3 PUFA supplementation. Age-related changes in the phospholipid PUFA content were also seen. Decreases in DHA were mostly corrected by supplementation. This study supports the neuroprotective effect of omega-3 fatty acids in brain ageing, and illustrates specific mechanisms underlying this effect.

20:5n-3 but not 22:6n-3 is a preferred substrate for synthesis of n-3 very-long- chain fatty acids (C24-C36) in retina

The objective of this study was to determine if 20:5n-3 or 22:6n-3 is the primary precursor of very-long-chain fatty acids (VLCFAs; C24-C36) synthesized in retina. Rats were fed semisynthetic, nutritionally complete diet containing 20% (w/w) fat with 3% (w/w) of 22:6n-3. After 6 weeks feeding, the vitreal fluid of each eye was injected with [3H]20:5n-3 or [3H]22:6n-3. Rats were then maintained under constant light (330 lux) or dark conditions for 48 hr. After 48 hr in vivo metabolism, the amount of label present in individual fatty acids was determined in major phospholipids in retina. For [3H]22:6n-3, 90% of total incorporation remained in 22:6n-3, whereas for [3H]20:5n-3 the label was actively incorporated into pentaenoic and hexaenoic VLCFAs up to 34 carbon chain length. 22:5n-3 derived from [3H]20:5n-3 was among the most highly labeled fatty acids. These observations suggest that 22:6n-3 is incorporated directly into retinal phospholipids without further metabolism, whereas 20:5n-3 and 22:5n-3 are metabolically active precursors for synthesis of VLCFAs.

Changes of the transcriptional and fatty acid profiles in response to n-3 fatty acids in SH-SY5Y neuroblastoma cells

Synthesis of docosahexaenoic acid (DHA) from its metabolic precursors contributes to membrane incorporation of this FA within the central nervous system. Although cultured neural cells are able to produce DHA, the membrane DHA contents resulting from metabolic conversion do not match the high values of those resulting from supplementation with preformed DHA. We have examined whether the DHA precursors down-regulate the incorporation of newly formed DHA within human neuroblastoma cells. SH-SY5Y cells were incubated with gradual doses of alpha-linolenic acid (alpha-LNA), EPA, or docosapentaenoic acid (DPA), and the incorporation of DHA into ethanolamine glycerophospholipids was analyzed as a reflection of synthesizing activity. The incorporation of EPA, DPA, and preformed DHA followed a dose-response saturating curve, whereas that of DHA synthesized either from alpha-LNA, EPA, or DPA peaked at concentrations of precursors below 15-30 microM and sharply decreased with higher doses. The mRNA encoding for six FA metabolism genes were quantified using real-time PCR. Two enzymes of the peroxisomal beta-oxidation, L-bifunctional protein and peroxisomal acyl-CoA oxidase, were expressed at lower levels than fatty acyl-CoA ligase 3 (FACL3) and delta6-desaturase (delta6-D). The delta6-D mRNA slightly increased between 16 and 48 h of culture, and this effect was abolished in the presence of 70 microM EPA. In contrast, the EPA treatment resulted in a time-dependent increase of FACL3 mRNA. The terminal step of DHA synthesis seems to form a "metabolic bottleneck," resulting in accretion of EPA and DPA when the precursor concentration exceeds a specific threshold value. We conclude that the critical precursor- concentration window of responsiveness may originate from the low basal expression level of peroxisomal enzymes.

Isolation and functional characterization of fatty acid delta5-elongase gene from the liverwort Marchantia polymorpha L

Bryophyte Marchantia polymorpha L. produces C22 very-long-chain polyunsaturated fatty acid (VLCPUFA). Thus far, no enzyme that mediates elongation of C20 VLCPUFAs has been identified in land plants. Here, we report the isolation and characterization of the gene MpELO2, which encodes an ELO-like fatty acid elongase in M. polymorpha. Heterologous expression in yeast demonstrated that MpELO2 encodes delta5-elongase, which mediates elongation of arachidonic (20:4) and eicosapentaenoic acids (20:5). Phylogenetic and gene structural analysis indicated that the MpELO2 gene is closely related to bryophyte Delta6-elongase genes for C18 fatty acid elongation and diverged from them by local gene duplication.

Cryptophyceae and rhodophyceae; chemotaxonomy, phylogeny, and application

The biochemical compositions of seven strains of marine cryptomonad and a rhodophyte were determined in logarithmic phase batch (1.4 L flask) and semi-continuous (10 L carboy) culture. Lipid ranged from 13% to 28%, protein ranged from 53% to 68%, and carbohydrate ranged from 9% to 24% of the organic weight. The major lipid classes in the species examined were polar lipids (78-88% of total lipid). The major sterol in the Cryptophyceae and the Rhodophyceae was 24-methylcholesta-5,22E-dien-3beta-ol (62-99% of total sterols); which is also the major sterol in some diatoms and haptophytes. Smaller proportions of cholest-5-en-3beta-ol (1-17.7%) were also found in the Cryptophyceae. Most cryptomonads contained high proportions of the n-3 polyunsaturated fatty acids (PUFA), 18:3n-3 (20.7-29.9% of the total fatty acids), 18:4n-3 (12.5-30.2%), 20:5n-3 (7.6-13.2%) and 22:6n-3 (6.4-10.8%). However, the blue-green cryptomonad Chroomonas placoidea was characterized by a low proportion of 22:6n-3 (0.2% of total fatty acids), and a significant proportion of 22:5n-6 (4.5%), and the presence of 24-ethylcholesta-5,22E-dien-3beta-ol (35.5% of total sterols). The fatty acid composition of the rhodophyte Rhodosorus sp. was similar to those of the Cryptophyceae except for lower proportions of 18:4n-3 and lack of C21 and C22 PUFA. It is postulated that the primary endosymbiosis of a photosynthetic n-3 C18 PUFA-producing prokaryote and a eukaryotic host capable of chain elongation and desaturation of exogenous PUFA, resulted in the Rhodophyceae capable of producing n-3 C20 PUFA. The secondary endosymbiosis of a photosynthetic n-3 C20 PUFA-producing eukaryote (such as a Rhodosorus sp. like-rhodophyte) and a eukaryotic host capable of further chain elongation and desaturation, resulted in the Cryptophyceae being capable of producing n-3 C20 and C22 PUFA de novo. Selected isolates were examined further in feeding trials with juvenile Pacific oysters (Crassostrea gigas). Rhodomonas salina CS-24(containing elevated 22:6n-3) produced high growth rates in oysters; equivalent to the microalga commonly used in aquaculture, Isochrysis sp. (T.ISO).

Peroxisome proliferator-activated receptor α is required for feedback regulation of highly unsaturated fatty acid synthesis

Delta6 desaturase (D6D), the rate-limiting enzyme for highly unsaturated fatty acid (HUFA) synthesis, is induced by essential fatty acid-deficient diets. Sterol regulatory element-binding protein-1c (SREBP-1c) in part mediates this induction. Paradoxically, D6D is also induced by ligands of peroxisome proliferator-activated receptor alpha (PPARalpha). Here, we report a novel physiological role of PPARalpha in the induction of genes specific for HUFA synthesis by essential fatty acid-deficient diets. D6D mRNA induction by essential fatty acid-deficient diets in wild-type mice was diminished in PPARalpha-null mice. This impaired D6D induction in PPARalpha-null mice was not attributable to feedback suppression by tissue HUFAs because PPARalpha-null mice had lower HUFAs in liver phospholipids than did wild-type mice. Furthermore, PPARalpha-responsive genes were induced in wild-type mice under essential fatty acid deficiency, suggesting the generation of endogenous PPARalpha ligand(s). Contrary to genes for HUFA synthesis, the induction of other lipogenic genes under essential fatty acid deficiency was higher in PPARalpha-null mice than in wild-type mice even though mature SREBP-1c protein did not differ between the genotypes. The expression of PPARgamma was markedly increased in PPARalpha-null mice and might have contributed to the induction of genes for de novo lipogenesis. Our study suggests that PPARalpha, together with SREBP-1c, senses HUFA status and confers pathway-specific induction of HUFA synthesis by essential fatty acid-deficient diets.

Infants with intrauterine growth restriction have impaired formation of docosahexaenoic acid in early neonatal life: a stable isotope study

This study evaluated the arachidonic acid (AA) and docosahexaenoic acid (DHA) formation from d5-labeled linoleic acid (d5-LA) and alpha-linolenic acid (d5-LNA) precursors in infants with intrauterine growth restriction (IUGR) compared with control groups matched by gestational age (GA) or birth weight. We compared DHA and AA formation from deuterated precursors d5-LA and d5-LNA in 11 infants with IUGR with 13 and 25 control subjects who were appropriate for GA and matched by GA and by birth weight, respectively. After an enteral administration of d5-LA and d5-LNA, we determined unlabeled and d5-labeled fatty acids at 24, 48, and 96 h in plasma. Absolute concentrations and area under the curve (AUC) over the 96-h study were used for analysis. Absolute concentration of d5-DHA and the product/precursor ratio of the d5-labeled AUCs indicated a less active DHA formation from LNA in infants with IUGR compared with their GA-matched (2-fold) and birth weight-matched (3-fold) control subjects. The ratios of eicosapentaenoic and n-3 docosapentaenoic acid to DHA were also affected. Similar evaluation for the n-6 series was not significant. DHA metabolism is affected in infants with IUGR; the restricted DPA to DHA conversion step seems to be principally responsible for this finding.

The role of essential fatty acids in development

The presence of docosahexaenoic acid (DHA) and arachidonic acid (ARA) in human milk but not in infant formula, coupled with lower plasma and brain lipid contents of DHA in formula-fed than in breast-fed infants and reports of higher IQ in individuals who were breast-fed versus formula-fed as infants, suggest that exogenous DHA (and ARA) may be essential for optimal development. Thus, since 1990, several studies have examined the impact of formulas containing DHA or DHA plus ARA on visual function and neurodevelopmental outcome. Some of these studies have shown benefits but others have not. These results leave largely unanswered the question of whether these fatty acids are beneficial for either the term or preterm infant. However, evidence that preterm infants might benefit is somewhat more convincing than that for term infants. Despite the limited evidence for efficacy, formulas supplemented with DHA and ARA are now available and appear to be safe.

Maternal dietary 22 : 6n-3 is more effective than 18 : 3n-3 in increasing the 22 : 6n-3 content in phospholipids of glial cells from neonatal rat brain

One of the debates in infant nutrition concerns whether dietary 18 : 3n-3 (linolenic acid) can provide for the accretion of 22 : 6n-3 (docosahexaenoic acid, DHA) in neonatal tissues. The objective of the present study was to determine whether low or high 18 : 3n-3 v. preformed 22 : 6n-3 in the maternal diet enabled a similar 22 : 6n-3 content in the phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI) and phosphatidylserine (PS) of glial cells from whole brain (cerebrum and cerebellum) of 2-week-old rat pups. At parturition, the dams were fed semi-purified diets containing either increasing amounts of 18 : 3n-3 (18 : 2n-6 to 18 : 3n-3 fatty acid ratio of 7.8 : 1, 4.4 : 1 or 1 : 1), preformed DHA, or preformed 20 : 4n-6 (arachidonic acid)+DHA. During the first 2 weeks of life, the rat pups from the respective dams received only their dam's milk. The fatty acid composition of the pups' stomach contents (dam's milk) and phospholipids from glial cells were quantified. The 20 : 4n-6 and 22 : 6n-3 content in the stomach from rat pups at 2 weeks of age reflected the fatty acid composition of the dam's diet. The 20 : 4n-6 content of PE and PS in the glial cells was unaffected by maternal diet treatments. Preformed 22 : 6n-3 in the maternal diet increased the 22 : 6n-3 content of glial cell PE and PS compared with maternal diets providing an 18 : 2n-6 to 18 : 3 n-3 fatty acid ratio of 7.8 : 1, 4.4 : 1 or 1 : 1 (P<0.0001). There was no significant difference in the 20 : 4n-6 and 22 : 6n-3 content of glial cell PC and PI among maternal diet treatments. It was concluded that maternal dietary 22 : 6n-3 is more effective than low or high levels of maternal dietary 18 : 3n-3 at increasing the 22 : 6n-3 content in PE and PS of glial cells from the whole brain of rat pups at 2 weeks of age. The findings from the present study have important implications for human infants fed infant formulas that are devoid of 22 : 6n-3.

In vivo conversion of 18- and 20-C essential fatty acids in rats using the multiple simultaneous stable isotope method

An important question for mammalian nutrition is the relative efficiency of C18 versus C20 essential fatty acids (EFAs) for supporting the tissue composition of n-3 and n-6 pathway end products. One specific question is whether C22 EFAs are made available to tissues more effectively by dietary alpha-linolenic acid (18:3n-3) and linoleic acid (18:2n-6) or by dietary eicosapentaenoic acid (20:5n-3) and dihomo-gamma-linolenic acid (20:3n-6). To address this question in a direct manner, four stable isotope compounds were given simultaneously in a novel paradigm. A single oral dose of a mixture of 2H5-18:3n-3, 13C-U-20:5n-3, 13C-U-18:2n-6, and 2H5-20:3n-6 was administered to rats given a defined diet. There was a preferential in vivo conversion of arachidonic acid (20:4n-6) to docosatetraenoic acid (22:4n-6) and of 22:4n-6 to n-6 docosapentaenoic acid (22:5n-6) when the substrates originated from the C18 precursors. However, when the end products docosahexaenoic acid (22:6n-3) or 22:5n-6 were expressed as the total amount in the plasma compartment divided by the dosage, this parameter was 11-fold greater for 20:5n-3 than for 18:3n-3 and 14-fold greater for 20:3n-6 than for 18:2n-6. Thus, on a per dosage basis, the total amounts of n-3 and n-6 end products accreted in plasma were considerably greater for C20 EFA precursors relative to C18.

Identification of two novel microalgal enzymes involved in the conversion of the omega3-fatty acid, eicosapentaenoic acid, into docosahexaenoic acid

Marine microalgae such as Pavlova and Isochrysis produce abundant amounts of the omega3-PUFAs (polyunsaturated fatty acids), EPA (eicosapentaenoic acid, 20:5n-3) and DHA (docosahexaenoic acid, 22:6n-3). The pathway leading to the conversion of EPA into DHA in these lower eukaryotes is not well established although it is predicted to involve an elongation step, catalysed by an elongating enzyme complex, leading to the conversion of EPA into omega3-DPA (omega-3-docosapentaenoic acid, 22:5n-3); followed by a desaturation step, catalysed by a Delta4-desaturase, which results in the conversion of DPA into DHA. To date, the enzymes involved in the elongation of EPA have not been identified from any lower eukaryote. In the present study, we describe the identification of microalgal genes involved in the two-step conversion of EPA into DHA. By expressed sequence tag analysis, a gene (pavELO) encoding a novel elongase was identified from Pavlova, which catalysed the conversion of EPA into omega3-DPA in yeast. Unlike any previously identified elongase from higher or lower eukaryotes, this enzyme displayed unique substrate specificity for both n-6 and n-3 C20-PUFA substrates, with no activity towards any C18- or C22-PUFA substrates. In addition, a novel Delta4-desaturase gene (IgD4) was isolated from Isochrysis, which was capable of converting omega3-DPA into DHA, as well as adrenic acid (22:4n-6) into omega6-DPA. Yeast co-expression studies, with pavELO and IgD4, revealed that these genes were capable of functioning together to carry out the two-step conversion of EPA into DHA.

Short-Term Carnitine Supplementation Does Not Augment LCPω3 Status of Vegans and Lacto-Ovo-Vegetarians

OBJECTIVE

Long-chain polyunsaturated omega-3 fatty acids (LCPomega3) synthesis, notably that of docosahexaenoic acid (DHA), from the precursor alpha-linolenic acid (ALA) proceeds with difficulty. We investigated whether carnitine supplementation augments the LCPomega3 status of apparently healthy vegans and lacto-ovo-vegetarians, who are expected to have low carnitine status.

METHODS

Group A (n = 11) took 990 mg/day l-carnitine from weeks 1-4, and 990 mg/day l-carnitine + 4 mL/day linseed oil from weeks 5-8. Group B (n = 9) took 4 mL/day linseed oil from weeks 1-4, and 4 mL/day linseed oil + 990 mg/day l-carnitine from weeks 5-8. Fatty acid compositions of red blood cells, platelets, plasma cholesterol esters and plasma triglycerides were measured in the fasting state at baseline, and after 4 and 8 weeks.

RESULTS

Carnitine supplementation increased plasma free and total carnitine concentrations with 30 and 25%, respectively, but did not affect eicosapentaenoic acid (EPA) and DHA contents of any of the investigated compartments. EPA and DHA changes were negatively related to initial carnitine status.

CONCLUSIONS

Our results suggest that carnitine is not an important limiting factor, if any, for LCPomega3 synthesis in vegans and lacto-ovo-vegetarians. This conclusion is also likely to apply to omnivores. The most efficient means to augment EPA and particularly DHA status remains consumption of LCPomega3 from e.g. fish or supplements.

Metabolic engineering of Arabidopsis to produce nutritionally important DHA in seed oil

Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are nutritionally important long-chain (≥ C20) omega-3 polyunsaturated fatty acids (ω3 LC-PUFA) currently obtained mainly from marine sources. A set of genes encoding the fatty acid chain elongation and desaturation enzymes required for the synthesis of LC-PUFA from their C18 PUFA precursors was expressed seed-specifically in Arabidopsis thaliana. This resulted in the synthesis of DHA, the most nutritionally important ω3 LC-PUFA, for the first time in seed oils, along with its precursor EPA and the ω6 LC-PUFA arachidonic acid (ARA). The assembled pathway utilised Δ5 and Δ6 desaturases that operate on acyl-CoA substrates and led to higher levels of synthesis of LC-PUFA than previously reported with acyl-PC desaturases. This demonstrates the potential for development of land plants as alternative sources of DHA and other LC-PUFA to meet the growing demand for these nutrients.

Vitamin A deficiency reduces liver and colon docosahexaenoic acid levels in rats fed high linoleic and low alpha-linolenic acid diet

Studies indicate that the transcription factor peroxisome proliferator-activated receptors (PPARs) regulate the activity of delta-6 and -5 desaturases and several key enzymes of peroxisomal beta-oxidation, including acyl-CoA oxidase. These enzymes are vital for the synthesis of docosahexaenoic (22:6 omega 3; DHA) and osbond (22:5 omega 6, OA) acids. An activated PPAR must form a hetrodimer with the obligate cofactor retinoid X receptor (RXR) to interact with a peroxisome proliferator responsive element (PPRE) of a target gene and to regulate transcriptional expression. The vitamin A metabolite, 9-cis retinoic acid, is the most potent ligand of RXR. We have tested the possibility that deficiency of vitamin A would compromise tissue levels of both DHA and OA in rats. Two groups of male Wistar rats were randomly distributed to receive vitamin A deficient (VAD) or sufficient (VAS) diet. After seven weeks of feeding, the rats were killed and colon and liver tissues removed for the analysis of fatty acids and antioxidant status. The VAD compared to the VAS rats had elevated levels of arachidonic (AA, P<0.001), adrenic acid (22:4 omega 6, P<0.005) and OA (P<0.0001) and reduced proportions of eicosapentaenoic (EPA, docosapentaenoic (DPA), DHA and total omega 3 fatty (P<0.0001) in colon choline phosphoglycerides (CPG). Similarly, liver CPG of the VAD rats had higher AA and adrenic acid and OA (P<0.0001), and lower EPA, DPA and DHA (P<0.0001) than the VAS rats. There was a similar fatty acid pattern in ethanolamine phosphoglycerides of the colon and liver tissues. These differences could not be explained by the conventional microsomal-peroxisomal pathway of the synthesis of the long-chain omega 6 and omega 3 polyunsaturated fatty acids. We postulate that deficiency of dietary vitamin A and the consequential depletion of retinoids inhibits DHA, and enhances OA, synthesis by differential effects on the independent synthetic pathways of the two fatty acids in the mitochondria. Various studies have documented that both DHA and vitamin A are vital for optimal visual and neural development and function. There is a need for further investigations to elucidate how vitamin A deficiency reduces membrane DHA level, and to delineate the synergistic effect of the two nutrients on vision, learning and memory.

Dietary 18:3ω3 influences immune function and the tissue fatty acid response to antigens and adjuvant

Alpha-linolenic acid (18:3omega3) has many important physiological functions including being beta-oxidized, serving a precursor to the synthesis of other lipids and it has immunomodulation properties. The objective of the present study was to test the effects of immunization and dietary 18:3omega3 on immune function and the fatty acid profile of immunized pig tissues. Piglets suckled from sows consuming either a control or high 18:3omega3 diet until 14 days old when they were weaned onto a similar diet as the sow and were moved to a segregated nursery for the remainder of the study. At 35 days of age, pigs on both diets (2 x 2 factorial design) received either an injection containing hen eggwhite lysozyme (HEWL), killed Mycobacterium tuberculosis and Freund's complete adjuvant (immunized) or phosphate buffered saline (PBS) (non-immunized) into the neck followed by a booster injection 2 weeks later and induction of delayed-type hypersensitivity (DTH) one week later. Immunization increased (compared to non-immunized) while the high 18:3omega3 diet decreased haptoglobin by 30% compared to pigs consuming the control diet. Immunized pigs had a seven-fold increase in antibodies to HEWL and pigs consuming the high 18:3omega3 diet also had transiently higher levels of serum antibodies. There was a diet by immunization interaction on the DTH reaction such that immunized pigs consuming the high 18:3omega3 had the largest DTH reaction. The neck muscle proximal to the site of injection of immunized pigs had 10-30% lower levels of triglyceride and phospholipid linoleic (18:2omega6) and 18:3omega3 compared to non-immunized pigs. Thus, a high 18:3omega3 intake in pigs modulates immune function and tissue fatty acids in response to immunization.

Structure, function, and dietary regulation of delta6, delta5, and delta9 desaturases

Fatty acid desaturases introduce a double bond in a specific position of long-chain fatty acids, and are conserved across kingdoms. Degree of unsaturation of fatty acids affects physical properties of membrane phospholipids and stored triglycerides. In addition, metabolites of polyunsaturated fatty acids are used as signaling molecules in many organisms. Three desaturases, Delta9, Delta6, and Delta5, are present in humans. Delta-9 catalyzes synthesis of monounsaturated fatty acids. Oleic acid, a main product of Delta9 desaturase, is the major fatty acid in mammalian adipose triglycerides, and is also used for phospholipid and cholesteryl ester synthesis. Delta-6 and Delta5 desaturases are required for the synthesis of highly unsaturated fatty acids (HUFAs), which are mainly esterified into phospholipids and contribute to maintaining membrane fluidity. While HUFAs may be required for cold tolerance in plants and fish, the primary role of HUFAs in mammals is cell signaling. Arachidonic acid is required as substrates for eicosanoid synthesis, while docosahexaenoic acid is required in visual and neuronal functions. Desaturases in mammals are regulated at the transcriptional level. Reflecting overlapping functions, three desaturases share a common mechanism of a feedback regulation to maintain products in membrane phospholipids. At the same time, regulation of Delta9 desaturase differs from Delta6 and Delta5 desaturases because its products are incorporated into more diverse lipid groups. Combinations of multiple transcription factors achieve this sophisticated differential regulation.

Moderate fish-oil supplementation reverses low-platelet, long-chain n-3 polyunsaturated fatty acid status and reduces plasma triacylglycerol concentrations in British Indo-Asians

BACKGROUND

The mechanisms involved in the increased mortality from coronary artery disease in British Indo-Asians are not well understood.

OBJECTIVES

This study aimed to investigate whether British Indo-Asian Sikhs have higher plasma triacylglycerol concentrations, lower platelet phospholipid levels, and lower dietary intakes of long-chain n-3 polyunsaturated fatty acids (PUFAs) than do age- and weight-matched Europeans and whether moderate dietary fish-oil intake can reverse these differences.

DESIGN

A randomized, double-blind, placebo-controlled, parallel, fish-oil intervention study was performed. After a 2-wk run-in period, 44 Europeans and 40 Indo-Asian Sikhs were randomly assigned to receive either 4.0 g fish oil [1.5 g eicosapentaenoic acid (EPA) and 1.0 g docosahexaenoic acid (DHA)] or 4.0 g olive oil (control) daily for 12 wk.

RESULTS

At baseline, the Indo-Asians had significantly higher plasma triacylglycerol, small dense LDL, apolipoprotein B, and dietary and platelet phospholipid n-6 PUFA values and significantly lower long-chain n-3 PUFAs (EPA and DHA) than did the Europeans. A significant decrease in plasma triacylglycerol, plasma apolipoprotein B-48, and platelet phospholipid arachidonic acid concentrations and a significant increase in plasma HDL concentrations and platelet phospholipid EPA and DHA levels were observed after fish-oil supplementation. No significant effect of ethnicity on the responses to fish-oil supplementation was observed.

CONCLUSIONS

Moderate fish-oil supplementation contributes to a reversal of lipid abnormalities and low n-3 PUFA levels in Indo-Asians and should be considered as an important, yet simple, dietary manipulation to reduce CAD risk in Indo-Asians with an atherogenic lipoprotein phenotype.

Type 1 diabetes compromises plasma arachidonic and docosahexaenoic acids in newborn babies

The activity of delta6- and delta5-desaturase, enzymes required for the synthesis of AA and DHA, are impaired in human and experimental diabetes. We have investigated whether neonates of type 1 diabetic women have compromised plasma AA and DHA at birth. Cord blood was obtained from healthy babies born to mothers with (n = 31) and without (n = 59) type 1 diabetes. FA composition of plasma choline phosphoglycerides (CPG), TG, and cholesterol esters (CE) was assayed. The neonates of the diabetics had lower levels of AA (20:4n-6, P< 0.0001), adrenic acid (22:4n-6, P < 0.01), sigman-6 metabolites (P < 0.0001), docosapentaenoic acid (22:5n-3, P < 0.0001), DHA (22:6n-3, P < 0.0001), sigman-3 (P < 0.0001), and sigman-3 metabolites (P< 0.0001) in CPG compared with the corresponding babies of the nondiabetic mothers. Similarly, they had lower levels of AA (P< 0.05), sigman-6 metabolites (P < 0.05), DHA (P< 0.0001), and sigman-3 metabolites (P< 0.01) in plasma CE. There was also a nonsignificant reduction of AA and DHA in TG in the babies of the diabetic group. The current investigation indicates that healthy neonates born to mothers with type 1 diabetes have highly compromised levels of AA and DHA. These nutrients are of critical importance for neurovisual and vascular system development. In poorly controlled maternal diabetes, it is conceivable that the relative "insufficiency" of AA and DHA may exacerbate speech and reading impairments, behavioral disorders, suboptimal performance on developmental tests, and lower IQ, which have been reported in some children born to mothers with type 1 diabetes mellitus. Further studies are needed to understand the underlying mechanism for this biochemical abnormality and its implications for fetal and infant development.

Dose effect of α-linolenic acid on PUFA conversion, bioavailability, and storage in the hamster

If an increased consumption of alpha-linolenic acid (ALA) is to be promoted in parallel with that of n-3 long-chain-rich food, it is necessary to consider to what extent dietary ALA can be absorbed, transported, stored, and converted into long-chain derivatives. We investigated these processes in male hamsters, over a broad range of supply as linseed oil (0.37, 3.5, 6.9, and 14.6% energy). Linoleic acid (LA) was kept constant (8.5% energy), and the LA/ALA ratio was varied from 22.5 to 0.6. The apparent absorption of individual FA was very high (>96%), and that of ALA remained almost maximum even at the largest supply (99.5%). The capacity for ALA transport and storage had no limitation over the chosen range of dietary intake. Indeed, ALA intake was significantly correlated with ALA level not only in cholesteryl esters (from 0.3 to 9.7% of total FA) but also in plasma phospholipids and red blood cells (RBC), which makes blood components extremely reliable as biomarkers of ALA consumption. Similarly, ALA storage in adipose tissue increased from 0.85 to 14% of total FA and was highly correlated with ALA intake. As for bioconversion, dietary ALA failed to increase 22:6n-3, decreased 20:4n-6, and efficiently increased 20:5n-3 (EPA) in RBC and cardiomyocytes. EPA accumulation did not tend to plateau, in accordance with identical activities of delta5- and delta6-desaturases in all groups. Dietary supply of ALA was therefore a very efficient means of improving the 20:4n-6 to 20:5n-3 balance.

Polyunsaturated fatty acids ameliorate hepatic steatosis in obese mice by SREBP-1 suppression

Leptin-deficient ob/ob mice show many characteristics of obesity, including excess peripheral adiposity as well as severe hepatic steatosis, at least in part, due to increased hepatic lipogenesis. Polyunsaturated fatty acids (PUFAs) are not only ligands for peroxisome proliferator-activated receptor (PPAR) alpha but are also negative regulators of hepatic lipogenesis, which is thought to be mediated by the repression of sterol regulatory element-binding protein (SREBP)-1. We have previously shown that the disruption of SREBP-1 in ob/ob mice decreased their liver triglyceride storage. To examine whether PUFAs could reduce hepatic triglyceride deposition, we challenged ob/ob mice with dietary PUFA. It is demonstrated that PUFA markedly decreased the mature form of SREBP-1 protein and thereby reduced the expression of lipogenic genes such as fatty acid synthase (FAS) and stearoyl-CoA desaturase 1 (SCD1) in the livers of ob/ob mice. Consequently, the liver triglyceride content and plasma alanine aminotransferase (ALT) levels were decreased. Furthermore, both hyperglycemia and hyperinsulinemia in ob/ob mice were improved by PUFA administration, similar to the effect of PPARalpha activators. In conclusion, PUFAs ameliorate obesity-associated symptoms, such as hepatic steatosis and insulin resistance, presumably through both down-regulation of SREBP-1 and activation of PPARalpha.

Docosahexaenoic acid affects insulin deficiency- and insulin resistance-induced alterations in cardiac mitochondria

The effect of docosahexaenoic acid (DHA) intake on cardiac mitochondrial function was evaluated in permeabilized fibers in insulin deficiency and insulin resistance in rats. The insulin-deficient state was obtained by streptozotocin injection 2 mo before investigations. Insulin resistance was obtained by feeding a 62% fructose diet for 3 mo. DHA was incorporated in the diet to modify the fatty acid composition of cardiac membranes, including mitochondria. Insulin deficiency decreased mitochondrial creatine kinase (mi-CK) activity and mitochondrial sensitivity to ADP. DHA intake prevented these alterations. Moreover, the insulin-deficient state significantly decreased n-3 polyunsaturated fatty acids (PUFA) and slightly increased n-6 PUFA in both cardiac and mitochondrial membranes, inducing a significant increase in the n-6-to-n-3 ratio. DHA intake maintained high myocardial and mitochondrial DHA content. Insulin deficiency also decreased glutamate- and palmitoylcarnitine-supported mitochondrial respiration, but DHA intake did not prevent these effects. In contrast, insulin resistance did not affect mi-CK activity or sensitivity to ADP. However, insulin resistance influenced the myocardial fatty acid composition with decreased n-6 and n-3 PUFA contents and increased monounsaturated fatty acid content. Only slight alterations were observed in mitochondrial fatty acid composition, and they were corrected by DHA intake. Moreover, insulin resistance decreased the glutamate-supported respiration, and DHA intake did not influence this effect. In conclusion, the impairment of cardiac mitochondrial function was more pronounced in the insulin-deficient state than in insulin resistance. The modification of fatty acid composition of cardiac and mitochondrial membranes by DHA partially prevented the mitochondrial alterations induced in the two models.

Effect of simvastatin on the uptake and metabolic conversion of palmitic, dihomo-gamma-linoleic and alpha-linolenic acids in A549 cells

It is well known that simvastatin affects cholesterol synthesis. Furthermore it inhibits growth and proliferation and perturbs fatty acid metabolism in some cell lines. We have studied the effects of simvastatin on the uptake and metabolism of exogenous fatty acid in the human lung adenocarcinoma A549 cells. Simvastatin inhibited the proliferation of A549, and caused an increment in phospholipid/cholesterol ratio due to an increment in phospholipid content without affecting cholesterol content. All the fatty acids were uptaken and metabolized in both control and treated cells. The conversion of palmitic, linoleic and dihomo-gamma-linoleic acids to their metabolites and products/precursor ratios for the desaturation and elongation reactions showed that simvastatin enhanced the Delta5 desaturation step and altered some elongating steps. The machinery for unsaturated fatty acid synthesis in A549 is quite sensitive to simvastatin and its effects could have important implication taking into account that highly unsaturated fatty acids are involved in the regulation of diverse cellular functions by themselves or through their metabolites.

Studies on the metabolic fate of n-3 polyunsaturated fatty acids

Several different processes involved in the metabolic fate of docosahexaenoic acid (DHA, C22:6n-3) and its precursor in the biosynthesis route, C24:6n-3, were studied. In cultured skin fibroblasts, the oxidation rate of [1-14C] 24:6n-3 was 2.7 times higher than for [1-14C]22:6n-3, whereas [1-14C]22:6n-3 was incorporated 7 times faster into different lipid classes than was [1-14C]24:6n-3. When determining the peroxisomal acyl-CoA oxidase activity, similar specific activities for C22:6(n-3)-CoA and C24:6(n-3)-CoA were found in mouse kidney peroxisomes. Thioesterase activity was measured for both substrates in mouse kidney peroxisomes as well as mitochondria, and C22:6(n-3)-CoA was hydrolyzed 1.7 times faster than C24:6(n-3)-CoA. These results imply that the preferred metabolic fate of C24:6(n-3)-CoA, after its synthesis in the endoplasmic reticulum (ER), is to move to the peroxisome, where it is beta-oxidized, producing C22:6(n-3)-CoA. This DHA-CoA then preferentially moves back, probably as free fatty acid, to the ER, where it is incorporated into membrane lipids.

Docosahexaenoic acid membrane content and mRNA expression of acyl-CoA oxidase and of peroxisome proliferator-activated receptor-delta are modulated in Y79 retinoblastoma cells differently by low and high doses of alpha-linolenic acid

The mRNA expression levels of acyl-CoA oxidase (AOX), a key enzyme in very-long-chain fatty acid peroxisomal oxidation, and of peroxisome proliferator-activated receptor-delta (PPAR-delta), a nuclear receptor possibly involved in the gene regulation of brain lipid metabolism, were determined in human Y79 retinoblastoma cells by using real-time quantitative polymerase chain reaction. Cells were dosed with alpha-linolenic acid (18:3n-3), the essential metabolic precursor of the n-3 polyunsaturated fatty acid series that normally gives rise through terminal peroxisomal oxidation to the synthesis of membrane docosahexaenoic acid (22:6n-3, or DHA). The AOX and PPAR-delta relative expression levels increased 2.3 and 3.4 times, respectively, upon dosing of cells with 7 microM 18:3n-3, whereas AOX cDNA abundance decreased by 50% upon dosing with 70 microM 18:3n-3. Concurrently, the DHA content increased by 23% in the membrane ethanolamine-phosphoglycerides from cells dosed with 7 microM 18:3n-3, whereas it decreased by 38% upon dosing with 70 microM 18:3n-3. The DHA's upstream precursors (20:5n-3 and 22:5n-3) both accumulated in cells dosed with 7 or 70 microM 18:3n-3. The 18:3n-3-induced changes in membrane phospholipid fatty acid composition support the hypothesis that the terminal peroxisomal step of n-3 conversion is rate limiting in the Y79 line. The concurrent 7 microM 18:3n-3-induced increase of mRNAs encoding for AOX and for PPAR-delta suggests that 18:3n-3 (or its metabolites) at low concentration could trigger its proper conversion to DHA, possibly through activation of PPAR-delta-mediated transcription of AOX. Decreased membrane DHA content and mRNA expression level of AOX in 70-microM 18:3n-3-dosed cells corroborated the relationship between AOX expression and DHA synthesis and suggested that simultaneous down-regulating events occurred at high concentrations of 18:3n-3.

Tissue deposition of n−3 FA pathway intermediates in the synthesis of DHA in rainbow trout (Oncorhynchus mykiss)

The tissue distribution of newly synthesized 22:6n-3 and intermediate PUFA was examined in rainbow trout to further our understanding of the metabolism of this EFA in fish. Rainbow trout were fed a pulse of deuterated linolenic acid (D5-17,17,18,18,18-18:3n-3), and the tissue distribution of deuterated anabolites was determined at intervals up to 35 d post-dose by GC-negative chemical ionization MS of the pentafluorobenzyl derivatives. D5-22:6n-3 was the major deuterated FA in liver and cecal mucosa 2 and 5 d post-dose. All the n-3 FA pathway intermediates were found in liver, cecal mucosa, and blood including D5-24:5n-3 and D5-24:6n-3. Brain and eyes also contained the full suite of intermediate deuterated FA, but with a different profile from liver when analyzed over a longer time course up to 35 d. D5-20:5n-3 was the major component in brain up to 7 d, after which D5-22:6n-3 became predominant, but D5-22:5n-3 constituted ca. 20% of FA throughout the time period. The pattern in eyes was similar but less pronounced. In visceral adipose tissue there was a much greater accumulation of the initial substrate, D5-18:3n-3, with D5-18:4n-3 and D5-22:6n-3 the predominant deuterated FA at all time points. There was a similar though less pronounced trend in eye socket adipose tissue. The C24 PUFA were not detected in visceral fat and barely detected in eye socket fat. The results show that the kinetics of accumulation and depletion of the various n-3 PUFA differ between tissues. The presence of pathway intermediate FA provides evidence that liver and ceca possess the full metabolic pathway for synthesis of 22:6n-3, whereas brain and eyes are less active, with an accumulation of pentaene intermediate FA, and adipose tissue is inactive.

Expression and regulation of delta5-desaturase, delta6-desaturase, stearoyl-coenzyme A (CoA) desaturase 1, and stearoyl-CoA desaturase 2 in rat testis

In mammalian cells, essential polyunsaturated fatty acids (PUFAs) are converted to longer PUFAs by alternating steps of elongation and desaturation. In contrast to other PUFA-rich tissues, the testis is continuously drained of these fatty acids as spermatozoa are transported to the epididymis. Alteration of the germ cell lipid profile from spermatogonia to condensing spermatids and mature spermatozoa has been described, but the male gonadal gene expression of the desaturases, responsible for the PUFA-metabolism, is still not established. The focus of this study was to characterize the expression and regulation of stearoyl-CoA desaturase 1 (SCD1), stearoyl-CoA desaturase 2 (SCD2), and Delta5- and Delta6-desaturase in rat testis. Desaturase gene expression was detected in testis, epididymis, and separated cells from seminiferous tubulus using Northern blot analysis. For the first time, SCD1 and SCD2 expression is demonstrated in rat testis and epididymis, both SCDs are expressed in epididymis, while testis mainly contains SCD2. Examination of the testicular distribution of Delta5- and Delta6-desaturase and SCD1 and SCD2 shows that all four desaturases seem to be localized in the Sertoli cells, with far lower expression in germ cells. In light of earlier published results showing that germ cells are richer in PUFAs than Sertoli cells, this strengthens the hypothesis of a lipid transport from the Sertoli cells to the germ cells. As opposed to what is shown in liver, Delta5- and Delta6-desaturase mRNA levels in Sertoli cells are up-regulated by dexamethasone. Furthermore, dexamethasone induces SCD2 mRNA. Insulin also up-regulates these three genes in the Sertoli cell, while SCD1 mRNA is down-regulated by both insulin and dexamethasone. Delta5- and Delta6-desaturase, SCD1, and SCD2 are all up-regulated by FSH. A similar up-regulation of the desaturases is observed when treating Sertoli cells with (Bu)2cAMP, indicating that the desaturase up-regulation observed with FSH treatment results from elevated levels of cAMP. Finally, testosterone has no influence on the desaturase gene expression. Thus, FSH seems to be a key regulator of the desaturase expression in the Sertoli cell.

Metabolism of stearidonic acid in human subjects: comparison with the metabolism of other n-3 fatty acids

BACKGROUND

For many persons who wish to obtain the health benefits provided by dietary n-3 fatty acids, daily ingestion of fish or fish oil is not a sustainable long-term approach. To increase the number of sustainable dietary options, a land-based source of n-3 fatty acids that is effective in increasing tissue concentrations of the long-chain n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is required.

OBJECTIVE

The objective of the study was to examine the ability of dietary stearidonic acid (SDA) to increase tissue concentrations of EPA and DHA in healthy human subjects and to compare the effectiveness of SDA with that of the n-3 fatty acids alpha-linolenic acid (ALA) and EPA.

DESIGN

Encapsulated SDA, ALA, or EPA was ingested daily in doses of 0.75 g and then 1.5 g for periods of 3 wk each by healthy male and postmenopausal female subjects (n = 15/group) in a double-blind, parallel-group design.

RESULTS

Dietary SDA increased EPA and docosapentaenoic acid concentrations but not DHA concentrations in erythrocyte and in plasma phospholipids. The relative effectiveness of the tested dietary fatty acids in increasing tissue EPA was 1:0.3:0.07 for EPA:SDA:ALA.

CONCLUSIONS

Vegetable oils containing SDA could be a dietary source of n-3 fatty acids that would be more effective in increasing tissue EPA concentrations than are current ALA-containing vegetable oils. The use of SDA-containing oils in food manufacture could provide a wide range of dietary alternatives for increasing tissue EPA concentrations.

Low serum cholesteryl ester-docosahexaenoic acid levels in Alzheimer's disease: a case-control study

Low n-3 polyunsaturated fatty acid (PUFA) status may be associated with neuro-degenerative disorders, in particular Alzheimer's disease, which has been associated with poor dietary fish or n-3 PUFA intake, and low docosahexaenoic acid (DHA) status. The present case-control study used an established biomarker of n-3 PUFA intake (serum cholesteryl ester-fatty acid composition) to determine n-3 PUFA status in patients with Alzheimer's disease, who were free-living in the community. All cases fulfilled the National Institute of Neurological and Communicative Disorders and Stroke and Alzheimer's Disease and Related Disorders Association criteria for Alzheimer's disease. Detailed neuropsychological testing and neuroimaging established the diagnosis in all cases. The subjects (119 females and twenty-nine males) aged 76.5 (SD 6.6) years had a clinical dementia rating (CDR) of 1 (SD 0.62) and a mini mental state examination (MMSE) score of 19.5 (SD 4.8). The control subjects (thirty-six females and nine males) aged 70 (SD 6.0) years were not cognitively impaired (defined as MMSE score <24): they had a mean MMSE score of 28.9 (SD 1.1). Serum cholesteryl ester-eicosapentaenoic acid and DHA levels were significantly lower (P<0.05 and P<0.001 respectively) in all MMSE score quartiles of patients with Alzheimer's disease compared with control values. Serum cholesteryl ester-DHA levels were progressively reduced with severity of clinical dementia. DHA levels did not differ in patients with Alzheimer's disease across age quartiles: all were consistently lower than in control subjects. Step-wise multiple regression analysis showed that cholesteryl ester-DHA and total saturated fatty acid levels were the important determinants of MMSE score and CDR. It remains to be determined whether low DHA status in Alzheimer's disease is a casual factor in the pathogenesis and progression of Alzheimer's disease.

Effect of the delta6-desaturase inhibitor SC-26196 on PUFA metabolism in human cells

The objective of this study was to determine the effect of 2,2-diphenyl-5-(4-[[(1 E)-pyridin-3-yl-methylidene]amino]piperazin-1-yl)pentanenitrile (SC-26196), a delta6-desaturase inhibitor, on PUFA metabolism in human cells. SC-26196 inhibited the desaturation of 2 microM [1-14C] 18:2n-6 by 87-95% in cultured human skin fibroblasts, coronary artery smooth muscle cells, and astrocytes. By contrast, SC-26196 did not affect the conversion of [1-14C]20:3n-6 to 20:4 in the fibroblasts, demonstrating that it is selective for delta6-desaturase. The IC50 values for inhibition of the desaturation of 2 microM [1-14C] 18:3n-3 and [3-14C]24:5n-3 in the fibroblasts, 0.2-0.4 microM, were similar to those for the inhibition of [1-14C 18:2n-6 desaturation, and the rates of recovery of [1-14C]18:2n-6 and [3-14C]24:5n-3 desaturation after removal of SC-26196 from the culture medium also were similar. SC-26196 reduced the conversion of [3-14C]22:5n-3 and [3-14C]24:5n-3 to DHA by 75 and 84%, respectively, but it had no effect on the retroconversion of [3-14C]24:6n-3 to DHA. These results demonstrate that SC-26196 effectively inhibits the desaturation of 18- and 24-carbon PUFA and, therefore, decreases the synthesis of arachidonic acid, EPA, and DHA in human cells. Furthermore, they provide additional evidence that the conversion of 22:5n-3 to DHA involves delta6-desaturation.

Fatty acid abnormalities in chronic pancreatitis: effect of concomitant diabetes mellitus

OBJECTIVE

Patients with chronic pancreatitis suffer from malabsorption and nutritional deficiencies. However there is little data available concerning the fatty acid profile in chronic pancreatitis. Diabetes mellitus, a common complication of this disease, could interfere with the metabolism of fatty acids.

SUBJECTS

We therefore compared the fatty acid composition of LDL from four groups of male patients with (a) chronic pancreatitis without diabetes (ND-CP; n=12), (b) diabetes secondary to chronic pancreatitis and insulin-treated (CP-D; n=35); (c) type 1 diabetes (n=25); and (d) controls (n=20).

RESULTS

The patients in both groups of chronic pancreatitis (ND-CP and CP-D) had lower mean values for linoleic acid than that seen in the type 1 DM and control groups, whereas monounsaturated fatty acids (MUFA; 18 : 1(n-9) and (16 : 1(n-7)) were significantly increased in these two groups (ND-CP and CP-D). Docosa-hexaenoic-acid (22 : 6(n-3)) was significantly decreased in the CP-D group (P>0.05), a response that could be explained by the effects of diabetes mellitus and by selenium deficiency. In this way, diabetes was associated with a decrease in the docosa-hexaenoic-acid (22 : 6(n-3); r=0.30, P=0.005), and selenium was correlated with DHA (r=0.28, P=0.029) and with the 22 : 6(n-3)/20 : 5(n-3) ratio (evaluating the delta 4 desaturation); r=0.31, P=0.022), independently of the diabetes effect. Selenium was negatively correlated with 20 : 4(n-6)/20 : 3(n-6) ratio (evaluating the delta 5 desaturase; r=-0.30; P=0.025). These results suggest that these two factors may have a role in the regulation of the desaturation process. If we consider that a ratio of 16 : 1(n-7)/18 : 2(n-6) greater than 0.086 in plasma indicates an EFAn-6 deficiency, 40% of our CP patients, 57.6% of CP-D patients and 13.6% of type 1 DM patients were involved.

CONCLUSIONS

The consequences of these deficiencies are not evaluated in this disease. However, correction of the fundamental deficiencies in essential fatty acids and in selenium seems desirable in chronic pancreatitis.

Hormonal modulation of delta6 and delta5 desaturases: case of diabetes

Animal biosynthesis of high polyunsaturated fatty acids from linoleic, alpha-linolenic and oleic acids is mainly modulated by the delta6 and delta5 desaturases through dietary and hormonal stimulated mechanisms. From hormones, only insulin activates both enzymes. In experimental diabetes mellitus type-1, the depressed delta6 desaturase is restored by insulin stimulation of the gene expression of its mRNA. However, cAMP or cycloheximide injection prevents this effect. The depression of delta6 and delta5 desaturases in diabetes is rapidly correlated by lower contents of arachidonic acid and higher contents of linoleic in almost all the tissues except brain. However, docosahexaenoic n-3 acid enhancement, mainly in liver phospholipids, is not explained yet. In experimental non-insulin dependent diabetes, the effect upon the delta6 and delta5 desaturases is not clear. From all other hormones glucagon, adrenaline, glucocorticoids, mineralocorticoids, oestriol, oestradiol, testosterone and ACTH depress both desaturases, and a few hormones: progesterone, cortexolone and pregnanediol are inactive.

Recent advances in the study of fatty acid desaturases from animals and lower eukaryotes

The biosynthesis of polyunsaturated fatty acids (PUFAs) in different organisms can involve a variety of pathways, catalyzed by a complex series of desaturation and elongation steps. A range of different desaturases have been identified to date, capable of introducing double bonds at various locations on the fatty acyl chain. Some recently identified novel desaturases include a delta4 desaturase from marine fungi, and a bi-functional delta5/delta6 desaturase from zebrafish. Using molecular genetics approaches, these desaturase genes have been isolated, identified, and expressed in variety of heterologous hosts. Results from these studies will help increase our understanding of the biochemistry of desaturases and the regulation of PUFA biosynthesis. This is of significance because PUFAs play critical roles in multiple aspects of membrane physiology and signaling mechanisms which impact human health and development.

Essential fatty acid synthesis and its regulation in mammals

The tissue content of highly unsaturated fatty acids (HUFA) such as arachidonic acid and docosahexaenoic acid is maintained in a narrow range by feedback regulation of synthesis. Delta-6 desaturase (D6D) catalyzes the first and rate-limiting step of the HUFA synthesis. Recent identification of a human case of D6D deficiency underscores the importance of this pathway. Sterol regulatory element binding protein-1c (SREBP-1c) is a key transcription factor that activates transcription of genes involved with fatty acid synthesis. We recently identified sterol regulatory element (SRE) that is required for activation of the human D6D gene by SREBP-1c. Moreover, the same SRE also mediates the suppression of the D6D gene by HUFA. The identification of SREBP-1c as a key regulator of D6D suggests that the major physiological function of SREBP-1c in liver may be the regulation of phospholipid synthesis rather than triglyceride synthesis. Peroxisome proliferators (PP) induce fatty acid oxidation enzymes and desaturases in rodent liver. However, the induction of desaturases by PP is slower than the induction of oxidation enzymes. This delayed induction may be a compensatory reaction to the increased demand of HUFA caused by increased HUFA oxidation and peroxisome proliferation in PP administration. Recent studies have demonstrated a critical role of peroxisomal beta-oxidation in DHA synthesis, and identified acyl CoA oxidase and D-bifunctional protein as the key enzymes.

Pyloric ceca are significant sites of newly synthesized 22:6n-3 in rainbow trout (Oncorhynchus mykiss)

In this pulse-chase study, rainbow trout fed a diet containing deuterated (D5) (17,17,18,18,18)-18:3n-3 ethyl ester accumulated D5-22:6n-3 in pyloric ceca to a greater extent than in liver 2 d post-dose. The ratio of newly synthesized D5-22:6n-3 in ceca to that in liver 2 d after feeding D5-18:3n-3 was 4.7 +/- 1.2 when expressed as per mg tissue and 5.2 +/- 2.4 when expressed as per mg protein. The amount of D5-22:6n-3 in ceca then declined whereas that in liver and blood increased, with the ratio of ceca to liver falling to 1.7 and 1.4, respectively, by day 5 and approaching unity by day 9. A crude cecal mucosa fraction contained 123 +/- 50 ng D5-22:6n-3/mg protein/mg D5-18:3n-3 eaten 2 d after feeding the tracer, compared with 35 +/- 21 ng D5-22:6n-3/mg protein/mg D5-18:3n-3 eaten in liver. Three days later the amount in cecal mucosa had fallen by one-third and that in liver had increased threefold. Most of the D5-18:3n-3 was catabolized very rapidly. The ratio of D5-18:3n-3 to 21:4n-6 (a relatively inert FA marker) in the diet was 4.0, but this fell to 0.30 in ceca and ca. 0.8 in liver, blood, and whole carcass one day after feeding. These results indicate that ceca are active in the synthesis of 22:6n-3 and the oxidation of 18:3n-3.

What is the role of alpha-linolenic acid for mammals?

This review examines the data pertaining to an important and often underrated EFA, alpha-linolenic acid (ALA). It examines its sources, metabolism, and biological effects in various population studies, in vitro, animal, and human intervention studies. The main role of ALA was assumed to be as a precursor to the longer-chain n-3 PUFA, EPA and DHA, and particularly for supplying DHA for neural tissue. This paper reveals that the major metabolic route of ALA metabolism is beta-oxidation. Furthermore, ALA accumulates in specific sites in the body of mammals (carcass, adipose, and skin), and only a small proportion of the fed ALA is converted to DHA. There is some evidence that ALA may be involved with skin and fur function. There is continuing debate regarding whether ALA has actions of its own in relation to the cardiovascular system and neural function. Cardiovascular disease and cancer are two of the major burdens of disease in the 21st century, and emerging evidence suggests that diets containing ALA are associated with reductions in total deaths and sudden cardiac death. There may be aspects of the action and, more importantly, the metabolism of ALA that need to be elucidated, and these will help us understand the biological effects of this compound better. Additionally, we must not forget that ALA is part of the whole diet and should be seen in this context, not in isolation.

Lipid metabolome-wide effects of the PPARgamma agonist rosiglitazone

Successful therapy for chronic diseases must normalize a targeted aspect of metabolism without disrupting the regulation of other metabolic pathways essential for maintaining health. Use of a limited number of single molecule surrogates for disease, or biomarkers, to monitor the efficacy of a therapy may fail to predict undesirable side effects. In this study, a comprehensive metabolomic assessment of lipid metabolites was employed to determine the specific effects of the peroxisome proliferator-activated receptor gamma (PPARgamma) agonist rosiglitazone on structural lipid metabolism in a new mouse model of Type 2 diabetes. Dietary supplementation with rosiglitazone (200 mg/kg diet) suppressed Type 2 diabetes in obese (NZO x NON)F1 male mice, but chronic treatment markedly exacerbated hepatic steatosis. The metabolomic data revealed that rosiglitazone i) induced hypolipidemia (by dysregulating liver-plasma lipid exchange), ii) induced de novo fatty acid synthesis, iii) decreased the biosynthesis of lipids within the peroxisome, iv) substantially altered free fatty acid and cardiolipin metabolism in heart, and v) elicited an unusual accumulation of polyunsaturated fatty acids within adipose tissue. These observations suggest that the phenotypes induced by rosiglitazone are mediated by multiple tissue-specific metabolic variables. Because many of the effects of rosiglitazone on tissue metabolism were reflected in the plasma lipid metabolome, metabolomics has excellent potential for developing clinical assessments of metabolic response to drug therapy.